Data processing apparatus



July 18, 1967 D 5, OLIVER 3,331,27fi

DATA PROCESSING APPARATUS Filed April 15, 1964 INVENTORS DONALD 5'. 0L IVER ATTORNEY United States Patent 3,331,276 DATA PROCESSlNG APPARATUS Donald S. Oliver, 13 Mohawk Drive,

' West Acton, Mass. 01780 Filed Apr. 15, MM, Ser. No. 360,009 25 Claims. (Cl. 88-24) This invention relates to a positive copy method and apparatus, and more particularly to a method and apparatus for making a positive copy using a copy medium that is photosensitive on both sides, and at least one side of which has a photoconductor as its photosensitive component.

Commonly owned copending Berman et al. application Ser. No. 199,211 filed May 14, 1962, the details of which are incorporated herein by reference, discloses copy media comprising photoconductive materials, i.e. materials having light activatable electrons, adaptable to use in the systems of the present invention. Exposure of such media to an image pattern of activating radiation renders chemically reactive those portions of the photoconductor media which are struck by radiation. The activated irradiated medium is next contacted with a developer system to effect a chemical redox reaction, on such contact, between the developer system and the activated chemically reactive portions of said medium. For example, according to the teachings of the copending application a filled or coated paper comprising a photoconductor such as titanium dioxide is exposed to an image pattern of radiation, and is then developed by simple contact with a developer system forming an image by redox reactions occurring at activated chemically reactive portions of the photoconductor. For example, the exposed medium may be contacted with a solution containing ions of a metal such as copper, silver, mercury or gold. The ions are reduced to free metal on contact with activated chemically reactive portions of the copy medium. Although exposures can be used which are suflicient to cause precipitation of such an amount of metal ion to free metal as will form a visible image in the copy medium, shorter exposure times can also be used. These result in the deposition of amounts of free metal which are insufficient to form visible images or which form images that are faint and light colored. Such faint latent developed images can be subsequently amplified by contact with developer systems of a type known in the silver halide photographic arts, for example, such as those comprising silver ion in admixture with a reagent forming a redox system, such as hydroquinone. Developer systems of this type tend to deposit further free metal on a surface where free metal is already present, and can be used in the present invention to amplify a previously formed latent developed image or can be used alone in a single developing step to form a visible image directly.

Images formed according to the technique just described will be negative images, that is, opaque portions will form in the print in lightstruck areas, i.e. those cor responding with translucent areas in the image pattern to be reproduced. Thus, prints obtained according to the process just described will be negatives of the desired image.

Among the general features of the systems according to copending patent application Ser. No. 199,211 that are important to the present invention are that the photoconductor of the photosensitive medium can be exposed to activating radiation and then deactivated so as to be image receptive upon subsequent exposure to activating radiveloped to form a visible image when desired, and a developed visible image can be chemically erased from the medium without harming the photoconductor. The photoconductors suitable for use with the present invention while sensitive to visible light can be deactivated and made image receptive by storage in darkness, heat, infra-red radiation, or corona discharge, as from a Tesla coil.

It is an object of the invention to make positive copies of original documents by simple and economic means.

Another object of the invention is to make a positive copy that is clear, has high resolution and contrast, and is simple, quick, and inexpensive to make.

Another object of the invention is to improve the quality of positive copies from original documents and decrease the cost of making such copies.

Another object of the invention is to make positive copies having negative copies on their reverse sides so that such positive copies can be recopied only by selected means.

Another object of the invention is to make positive copies of an original document on an erasable and reusable medium the photosensitive component of which is a photoconductor.

To these and other ends the invention resides in certain improvements, procedures, and combinations of parts, all as will be hereinafter more fully described, the novel features being pointed out in the claims at the end of the specification.

The drawings show partially schematic, partially sectioned side views of copying apparatus according to the invention and indicate in FIG. 1 a first path of travel of a copy medium through the apparatus and in FIG. 2 a second path of travel of a copy medium through the apparatus.

Generally, a positive copy is produced according to the invention by forming a latent negative image of an original document on one photosensitive side of a copy medium, developing the negative image, deactivating the photoconductor on the other side of the copy medium, and exposing the latter to radiation passing through the developed negative image so as to form a positive latent image of the original document, and then developing the positive latent image to form a positive copy of the original document. The negative image on the back of the positive copy can be underdeveloped so as to be faint, can be chemically erased, or can be left black.

The apparatus of FIGS. 1 and 2 is illustrative only and is selected for showing one practical variant of the many possible arrangements of apparatus according to the invention. Generally, the copier 10 shown in the drawings is for making a positive copy of an original document and is suitable for use in businesses, ofiices, libraries, schools, and other places Where positive copies of documents are desired.

In the illustrated copier 10, a sheet of a copy medium is fed through a plurality of processing stations. Means for such feeding of a sheet are Well known in the sheet feeding arts and are merely incidental to the present invention. Accordingly, the sheet feeding means of the illustrated copier is shown somewhat schematically as rollers, hips, and guides, but it will be understood that belts, frames, conveyors, suction or airs-tream devices and other sheet feeding devices can also be adapted to feeding sheets through apparatus according to the invention by those skilled in the sheet feeding arts. Also, synchronization of movements of drive rollers, switches, processing stations, energization and de-energization of heaters, and light sources, can all be controlled by timing means Well known to persons skilled in the art.

A copy medium photosensitive on both sides is used in the practice of the invention, A first side of such copy medium is used for forming the negative image of an original document to be copied and can be any of a number of well known photosensitive coatings or surfaces including a photoconductive coating. The second side of the copy medium is used for forming the positive image of the document and in accordance with the invention has original document from which a positive image is subsequently made on the opposite side of the copy medium.

Copy media can also be formed having a photoconductor as the photosensitive component of each side. Such media can be handled as ordinary paper and exposed to normal room and outdoor light. This is possible because the photoconductor can be deactivated by dark storage, heating, infra-red radiation, or corona discharge and thereby made image receptive before exposure.

The copier is adapted for deactivating a photoconductive coating before the second exposure of the copy medium to produce the positive image, and the copiers deactivating means can easily be operated for deactivating a photoconductive coating before the first exposure of the copy medium. Therefore, it is preferred that a copy medium having a photoconductor as the photosensitive component of each side be used in the inventive system and apparatus so as to obtain the advantages of handling the copy medium as ordinary paper exposable to light without damage. Accordingly, the invention will be described for the use of a copy medium having a photoconductive coating on each side, although it will be understood that the invention is not limited to such a medium, Typical preferred photocond uctive coatings are described in the previously mentioned copending application.

In the illustrated embodiment of the invention a copier 10 has an entrance 11 in the form of a slot into which a sheet of copy medium according to the invention and an original document to be copied can be fed for making a positive copy. An ordinary document is preferably laid face down on the copy medium so as to contact the upper or first side of the copy medium. In simple well known ways the inside of the machine 10 is kept dark or relatively dark, and particularly excludes ambient ultraviolet radiation with respect to which the photoconductor of the preferred copy medium is especially sensitive.

Close inside the entrance 11 of the copier 10 is a photoconductor deactivation station for making the photoconductor of the copy medium image receptive. As mentioned above, the copy medium preferred for use in the invention can be deactivated by dark storage, heat, infrared radiation, or corona discharge, but a simple electric heater is convenient, inexpensive, reliable, and preferred for deactivating the photoconductor of the copy medium. Heater 12 can be positioned on either side of the copy medium but preferably supplies sufficien-t heat for erasing any fogging, latent image, or activation of the photoconductor on either side of the copy medium from previous exposure to radiation so that each side of the copy medium is image receptive and uniformly activatable by radiation.

Since a hot photoconductive layer cannot be activated by radiation, the photoconductor of the copy medium must be cooled somewhat before exposure, and this is preferably accomplished by passing the medium over heat conducting plate 13 and between heat conducting drive rollers 14 and 15 that conduct heat away from th medium.

Next, the copy medium and the document to be copied are fed to an exposure station 16 where they pass under platen 17 and are exposed to radiation directed upwardly from light source 18. Light source 18 is preferably a source of ultraviolet light or radiation to which the photoconductor of the copy medium is especially sensitive. Radiation from source 18 passes through the copy medium to the superimposed document for reflex printing a negative latent image of the original document on the top or first side of the copy medium. Other methods, including optical and contact printing of an image of an original document on a copy medium are known and usable in the practice of the invention, but in the illustrated copier, reflex printing is preferred for its simplicity and effectiveness. The reflex printing of the latent negative image of the original document and the photoconductor of the copy medium can be accomplished as the copy medium and the original document pass through the exposure station 16.

Beyond exposure station 16, a guide 19 directs the original document into an exit path 20 and allows the copy medium to proceed straight ahead to further processing stations.

The copy medium the top or first side of which bears a latent negative image of the original document is then fed to a developing station 21 Where such image is developed.

Developer station 21 is shown schematically as having two units for applying preferably liquid developer, although a single developer application is possible, and three or more developer applications may be made at the developing station. 21 as described above and as set out in copending application Ser. No. 199,211. In the illustrated embodiment, the first developer application corresponds to contacting the medium with a solution containing preferably silver ions for depositing free metal on the medium, as described above, and the second developer application corresponds to an amplifying developer system.

Since the negative image on the first side of the copy medium is not intended to provide the final copy, and need not be permanent, it is not necessary to fix the developed negative image. Accordingly, copy medium hearing a developed negative image can be shunted or diverted to a lower path 25 by a movable switch 24 positioned in its solid line position as illustrated in FIG. 1 so that the copy medium does not pass through fixing station 32. The shunt path of the copy medium downward from switch 24 is shown by arrows in FIG. 1. Mechanical switch 34 is positioned in its solid line position as illustrated in FIG. 1 to allow the copy medium to be fed straight along lower path 25 and then downward into reversing chamber 26 where its leading edge contacts movable arm 28 of electric switch 27 and moves arm 28 to the position illustrated in FIG. 2 for actuating switch 27. Actuation of switch 27 reverses the direction of drive of reversing rollers 29 and 30 and changes the positions of mechanical switches 24 and 34 so that the copy medium can be fed upward through path 31 and then through the copier 10 in a second circuit path as illustrated by arrows in FIG. 2.

On the second or.return trip of the copy medium through the stations of copier 10, the copy medium is inverted so that its first or negative image side is downward and its second or former bottom side is upward.

As shown by the arrow path of FIG. 2 the copy medium is fed through a similar sequence of processing stations on its return trip during which a positive image is formed of the developed negative image on the first side of the medium. On such return trip the copy medium first passes over heater 12 which, as described above, deactivates the photoconductor of the medium in the same way that the medium was initially deactivated when first inserted in copier 10. The copy medium then passes over cooling plate 13 and through cooling rollers 14 and 15 and into exposure station 16 as previously described.

At exposure station 16, the copy medium is exposed to upwardly directed radiation from source 18 which passes through the developed negative image on the bottom side of the copy medium and exposes the deactivated photoconductor on the top or second side of the copy medium to an image pattern of activating radiation to form a positive latent image of the original document in the photo conductor on the second side of the copy medium.

Upon leaving exposure station 16, the copy medium is fed to developer station 21 where the above described image development occurs for producing a visible positive image on the top side of the copy medium.

Switch 24, on the second trip of the copy medium through copier is in its solid line upward position as illustrated in FIG. 2 so as to allow the copy medium to pass to fixing station 32 where the developed position image is fixed. Fixing at station 32 is preferably accomplished by contacting the developed positive image on the copy medium with a liquid fixing solution. Although fixing station 32 is shown schematically as a single unit, it can also comprise a plurality of liquid applications including fixes and washes and including means for drying the copy medium.

Opposite fixing station 32 is a bleaching station 33 for chemically erasing the developed negative image from the bottom or back side of the copy medium. Bleaching station 33 is preferred for the illustrated embodiment where the negative image is as fully developed as the positive image and hence dark. For some purposes, such as for preventing copying of the positive copy except by optical means, the dark negative image can be left on the reverse side of the positive copy, but for most purposes, chemical bleaching of the negative image of the back of the positive copy is more satisfactory.

Bleaching systems are well known for erasing or lightening the negative image on the back of the positive copy. For example if silver images have been formed, silver bleaching systems are well known in the photographic arts, and include for example, potassium ferricyanide bleaches and aqueous solutions of hydrogen peroxide.

After the copy medium passes fixing station 32, it is directed downward to lower path 25 where mechanical switch 34 is in its solid upper position as shown in FIG. 2 for directing the copy medium upward toward exit path 20 out of copier 10 and into a copy receiving bin 35.

The illustrated copier 10 can easily be modified to make positive copies according to another preferred form of the invention. As mentioned above, it is preferred that the negative image on the back side of the positive copy be invisible or only faintly visible. To accomplish this the negative latent image can be underdeveloped so that less silver or other metal is deposited on the copy medium and the resulting image can be a light color such as champagne or sandy beige. Such a faint image is nevertheless suitable for exposing a positive image on the second run of the copy medium through the copier 10.

Controlled underdeveloping of the negative image of the copy medium can be accomplished by increasing the speed of passage of the copy medium through developer station 21 or by varying the development applied at station 21. A preferred way of controlling the underdevelopment of the negative image is by-eliminating an application of liquid developer such as at station 23. Thus, for example, the exposed copy medium can be contacted with a methanolic or aqueous solution of silver nitrate, such as development corresponding to the schematically illustrated developer station 22. Then rather than amplifying such development at station 23 by further deposition of silver on the copy medium, the shunt or diversion path leading downward from switch 24 can be moved to a position between stations 22 and 23. The excess silver ions absorbed on the paper from the application of station 22 can be removed by treating the medium with a pure solvent applied at a station positioned on the downward shunt path leading from switch 24. By such a relocation of the shunt path for the copy mediums first run through copier 10, the negative image receives one development application and preferably a wash, and the positive image receives development, amplification of development, and fixing. By such an arrangement, the negative image on the back of the positive copy is faint and light colored enough so that bleaching station 33 can be omitted.

While the invention has been disclosed herein by reffirst and second sides each of erence to the details of a preferred embodiment, it is to be understood that such disclosure is intended in an illustrative, rather than a limiting sense, and it is contemplated that various modifications of the procedures, construction, and arrangement of the parts will readily occur to those skilled in the art within the spirit of the invention and the scope of the appended claims.

I claim:

1. A document copying system comprising in combination: a copy medium having first and second sides each of which are photosensitive and at least said second side of said medium having a photoconductor as the photosensitive component thereof; means for exposing said first side of said medium to activating radiation in animage pattern corresponding to an original document to be copied so as to form on said first side a negative latent image of said original document; means for developing said negative latent image; means for uniformly deactivating said photoconductor on said second side of said medium; means for exposing said photoconductor on said second side to activating radiation in the pattern of said developed negative image so as to form a positive latent image of said original document; and means for developing said positive latent image to produce a positive copy of said original document.

2. The document copying system of claim 1 wherein said deactivating photoconductor.

3. A document copying system comprising in combination: a copy medium having first and second sides respectively coated with first and second photosensitive layers each of which comprises a photoconductor; means for uniformly deactivating said first side photoconductor; means for exposing said first side photoconductor to activating radiation in an image pattern corresponding to an original document to be copied so as to form in said first side photoconductor a negative latent image of said original document; means for developing said negative latent image; means for uniformly deactivating said second side photoconductor; means for exposing said second side photoconductor to activating radiation having the image pattern of said developed negative image so as to form in said second side photoconductor a positive latent image of said original document; and means for developing said positive latent image to produce a positive copy of said original document.

4. The document copying system of claim 3 wherein each of said deactivating means comprises means for heating said photoconductive layers.

5. The document copying system of claim 4 wherein a single heater for simultaneously heating each of said photoconductive layers comprises each of said deactivating means.

6. A positive copier for using a copy medium having which are photosensitive and at least said second side of said medium having a photoconductor as the photosensitive component thereof, said copier comprising; a plurality of processing stations; means for feeding said copy medium sequentially through said processing stations; a first one of said stations comprising means for exposing said first side of said copy medium to activating radiation for producing a means comprises means for heating said negative latent image of said original document on said first side of said copy medium, a second one of said processing stations comprising means for developing said negative latent image; a third one of said processing stations comprising means for uniformly deactivating said second side photoconductor; a fourth one of said processing stations comprising means for exposing said deactivated second side photoconductor to activating radiation for forming a positive latent image of said original document in said second side photoconductor; and a fifth one of said processing stations comprising means for developing said positive latent image to produce a positive copy of said original document.

7. A copier according to claim 6 wherein said deactivating means comprises means for heating said second side photoconductor.

8. A copier according to claim 7 wherein each of said developing means comprises means for contacting said medium with a liquid developing agent.

9. A positive copier for usinga copy medium having a first and second sides respectively coated with first and second photosensitive layers each of which comprises a photoconductor, said copier comprising: a plurality of processing stations; means for feeding said copy medium sequentially through said processing stations; a'first one of said stations comprising means for uniformly deactivating said first side photoconductor; a second one of said stations comprising means for exposing said first side photoconductor to activating radiation for producing a negative latent image of said original document in said first side photoconductor; a third one of said processing stations comprising means for developing said negative latent image; a fourth one of said processing stations comprising means for uniformly deactivating said second side photoconductor; a fifth one of said processing stations comprising means for exposing said deactivated said second side photoconductor to activating radiation for forming a positive latent image of said original document in said second side photoconductor; and a sixth one of said processing stations comprising means for developing said positive latent image to produce a positive copy of said original document. a

10. A copier according to claim 9 wherein each of said deactivating means comprises means for heating said medium, and each of said developing means comprises means for contacting said medium with a liquid developing agent.

11. The copier of claim 9 wherein said second station comprises means for reflex printing said negative image in said first side photoconductor.

12. A copier according to claim 9 wherein a seventh one of said processing stations comprises means for bleaching said developed negative image.

13. A copier according to claim 9 wherein said negative image is underdeveloped so as to form a faintly visible image.

14. A positive copier for using a copy medium having first and second sides each of which are photosensitive and at least said second side of said medium having a photoconductor as the photosensitive component thereof, said copier comprising: a plurality of processing stations; means for feeding said copy medium through said stations in a first sequence of stations and a second sequence of stations; said first sequence of stations comprising (a) means for exposing said first side of said copy medium to activating radiation for producing a negative latent image of said original document on said first side of said copy medium, and

(b) means for developing said negative latent image.

and

said second sequence of stations comprising (c) means for uniformly deactivating said photoconductor on said second side of said copy medium,

((1) means for exposing said photoconductor on said second side of said copy medium to activating radiation in the image pattern of said developed negative image for forming a positive latent image of said original document in said photoconductor on said second side of said copy'medium, and

(e) means for developing said positive latent image to produce a positive copy of said original document.

15. A copier according to claim 14 wherein theexposure means of paragraphs (a) and (d) comprise a single radiation source.

17. A positive copier for using a copy medium having first and second sides respectively coated with first and second photosensitive layers each of which comprises a photoconductor, said copier comprising: a plurality of processing stations; means for feeding said copy medium a through said stations in a first sequence of stations and a (e) means for exposing said sec-ond side photoconductor to activating radiation in the image pattern of said developed negative image for producing a positive latent image of said original document in said second side photoconductor, and

(f) means for'developing said positive latent image to produce a positive copy of said original document.

18. A copier according to claim 17 wherein the means of paragraphs (a) and (d) comprise a single means for heating said medium.

19. A copieraccording to claim 18 wherein the means of paragraphs (b) and (e) comprise a single source of radiation.

20. A copier according to claim 19 wherein the means of paragraphs (0) and (f) comprise means for contacting said medium with a liquid developing agent.

21. A positive copier for using a copy medium having first and second sides respectively coated with firstand second photosensitive layers each of which comprises a photoconductor, said copier comprising:- a plurality of processing stations; means for feeding said copy medium through said stations in a first sequence of stations and a second sequence of stations; said first sequence of stations comprising (a) means for uniformly deactivating said first side photoconductor,

(b) means for exposing said first side photoconductor to activating radiation for producing a negative latent image of said original document in said first side photoconductor, and

(c) means for developing said negative latent image,

and

said second sequence of stations comprising ((1) means for uniformly deactivating said second side photoconductor,

(e) means for exposing said second side photoconductor to activating radiation in the image pattern of said developed negative image for producing a positive latent image of said original document in said second side photoconductor,

(f) means for developing said positive latent'image,

and

(g) means for fixing said developed positive image to produce a positive copy of said original document.

22. A positive copier for using a copy medium having first and second sides respectively coated with first and second photosensitive layers each of which comprises a photoconductor, said copier comprising: a plurality of processing stations; means for feeding said copy medium through said stations in a first sequence of stations and a second sequence of stations; said first sequence of stations comprising (a) means for uniformly deactivating said first side photoconductor, (b) means for exposing said first side photoconductor to activating radiation for producing a negative latent image of said original document in said first side photoconductor, and

(c) means for developing said negative latent image,

and

said second sequence of stations comprising ((1) means for uniformly deactivating said second side photoconductor,

( e) means for exposing said second side photoconductor to activating radiation in the image pattern of said developed negative image for producing a positive latent image of said original document in said second side photoconductor,

(f) means for developing said positive latent image,

(g) means for fixing said developed positive image to produce a positive copy of said original document, and

(h) means for bleaching said developed negative image.

23. A positive copier for using a copy medium having first and second sides respectively coated with first and second photosensitive layers each of which comprises a photoconductor, said copier comprising: a plurality of processing stations; means for feeding said copy medium through said stations in a first sequence of stations and a second sequence of stations; said first sequence of stations comprising- (-a) means for uniformly deactivating said first side photoconductor,

(b) means for exposing said first side photoconductor to activating radiation for producing a negative latent image of said original document in said first side photoconductor, and

(c) means for underdeveloping said negative latent image, and

said second sequence of stations comprising-- (d) means for uniformly deactivating said second side photoconductor,

(e) means for exposing said second side photoconductor to activating radiation in the image pattern of said developed negative image for producing a positive latent image of said original document in said second side photoconductor,

(f) means for developing said positive latent image, and

(g) means for fixing said developed positive image to produce a positive copy of said original document.

24. A positive copier for using a copy medium having first and second sides respectively coated with first and second photosensitive layers each of which comprises a photoconductor, said copier comprising: a plurality of processing stations; means for keeping ambient activating radiation from said processing stations; means for feed ing a sheet of said copy medium and a superimposed original document to be copied through a first sequence of stations comprising- (a) heating means for uniformly deactivating said first side photoconductor, and

(b) ultraviolet radiating means disposed beneath said medium for directing radiation upward through said medium so as to reflex print a negative latent image of said original document on said first side photoconductor,

means beyond said radiating means for feeding said original document from said copier; means for feeding said copy medium through said stations in a second sequence of stations and a third sequence of stations; said second sequence of stations comprisingmeans for contacting said first side photoconductor with a liquid developing agent,

((1) means for inverting said medium so that said medium is fed through said second sequence of stations in a reversed side orientation, and said third sequence of stations comprising-- (e) said heating means of paragraph (a) for uniformly deactivating said second side photoconductor,

(f) said ultraviolet radiation means of paragraph (b) disposed beneath said medium for directing radiation upward through said developed negative image for forming a positive latent image of said original document in said second side photoconductor,

(g) said means of paragraph (c) for contacting said second side photoconductor with a liquid developing agent,

(h) means for fixing said developed positive image to produce a positive copy of said original document,

(i) means for bleaching said developed negative image,

and

(j) means for feeding said positive copy from said copier.

25. A positive copier for using a copy medium having first and second sides respectively coated with first and second photosensitive layers each of which comprises a photoconductor, said copier comprising: a plurality of processing stations; means for keeping ambient activating radiation from said processing stations; means for feeding a sheet of said copy medium and a superimposed original document to be copied through a first sequence of stations comprising (a) heating means for uniformly deactivating said first side photoconductor, and

(-b) ultraviolet radiating means disposed beneath said medium for directing radiation upward through said medium so as to reflex print a negative talent image of said original document on said first side photoconductor,

means beyond said radiating means for feeding said original document from said copier; means for feeding said copy medium through said stations in a second sequence of stations and a third sequence of stations; said second sequence of stations comprising (c) means for contacting said first side photoconductor with a liquid developing agent,

(d) means for inverting said medium so that said medium is fed through said second sequence of stations in a reversed side orientation,

and said third sequence of stations comprising (e) said heating means of paragraph (a) for uniformly deactivating said second side photoconductor,

(f) said ultraviolet radiation means of paragraph (b) disposed beneath said medium for directing radiation upward through said developed negative image for forming a positive latent image of said original document in said second side photoconductor,

(g) said means of paragraph (c) for contacting said second side photoconductor with a liquid developing agent,

(h) means for contacting said second side photoconductor with a liquid agent for amplifying said latent developed image to form a developed positive image,

(i) means for fixing said developed positive image to produce a positive copy of said original document, and

(j) means for feeding said positive copy from said copier.

No references cited.

NORTON ANSHER, Primary Examiner. R. A. WINTERCORN, Assistant Examiner. 

1. A DOCUMENT COPYING SYSTEM COMPRISING IN COMBINATION: A COPY MEDIUM HAVING FIRST AND SECOND SIDES EACH OF WHICH ARE PHOTOSENSITIVE AND AT LEAST SAID SECOND SIDE OF SAID MEDIUM HAVING A PHOTOCONDUCTOR AS THE PHOTOSENSITIVE COMPONENT THEREOF; MEANS FOR EXPOSING SAID FIRST SIDE OF SAID MEDIUM TO ACTIVATING RADIATION IN AN IMAGE PATTERN CORRESPONDING TO AN ORIGINAL DOCUMENT TO BE COPIED SO AS TO FORM ON SAID FIRST SIDE A NEGATIVE LATENT IMAGE OF SAID ORIGINAL DOCUMENT; MEANS FOR DEVELOPING SAID NEGATIVE LATENT IMAGE; MEANS FOR UNIFORMLY DEACTIVATING SAID PHOTOCONDUCTOR ON SAID SECOND SIDE OF SAID MEDIUM; MEANS FOR EXPOSING SAID PHOTOCONDUCTOR ON SAID SECOND SIDE TO ACTIVATING RADIATION IN THE PATTERN OF SAID 